The present invention relates to an internal combustion engine for automobiles or the like, more particularly to a cylinder head structure defining the upper part of an engine body of an internal combustion engine.
Typically, in a combustion chamber for each cylinder of an internal combustion engine, an intake port is provided with an intake valve for opening/closing the intake port to induct an air or mixture into the combustion chamber, while an exhaust port is provided with an exhaust port for opening/closing the exhaust port to discharge an expanded combustion gas from the combustion chamber. Currently, for valve mechanisms for driving and/or controlling the opening/closing motions of such intake and exhaust valves, there are widely used various types including an overhead-valve (OHV) type wherein a camshaft is arranged in the side region of a crankcase, a single overhead camshaft (SOHC) type wherein a camshaft is arranged in the upper region of a cylinder head and the intake and exhaust valves are driven by a single camshaft, or a double overhead camshaft (DOHC) type wherein a camshaft is arranged in the upper region of a cylinder head and the intake and exhaust valves are driven separately by individual camshafts.
As compared to the OHV engine, the SOHC and DOHC engines are superior in high-speed performance. Conversely, relatively long distance between the camshaft and crankshaft of the SOHC and DOHC engines can lead to a complicated driving arrangement of the camshaft and a complicated cylinder head structure.
The valves of the SOHC engine are driven indirectly by the camshaft through a rocker arm. In contrast, the valves of the DOHC engine are driven directly by the camshaft. In the DOHC engine, a tappet or lifter is employed as a follower element which is contacted continuously with the cam surface of the camshaft so as to convert the rotational motion of the cam into the reciprocating motion to be transferred to the valves. As a carrying element for containing and guiding the tappet, a tappet guide or lifter guide is formed integrally with the cylinder head by casting, or otherwise is separately formed and then incorporated in the cylinder head.
On the other hand, each of bearing portions each having a journal portion for supporting the camshaft is comprised of a vertical wall portion protruding vertically from the base portion of the cylinder head and a cam cap coupled with the vertical wall portion. The vertical wall portion is formed integrally with the cylinder head by casting, or otherwise is separately formed and then incorporated in the cylinder head. In order to assure the supporting rigidity of the camshaft, the bearing portion is arranged close to the cam located for each valve.
Taking a four-valve type engine having a pair of intake ports and intake valves and a pair of exhaust ports and exhaust valves for each cylinder as an example, a pair of intake valve driving cams or a pair of exhaust valve driving cams are aligned on the camshaft. Two adjacent bearing portions are located on both sided of the pair of intake valve cams or the pair of exhaust valve cams with interposing these cams between the bearing portions, and more specifically each bearing portion is located in the outboard region of a cylinder and between said cylinder and another cylinder adjacent to said cylinder. Otherwise, each bearing portion is located between the pair of intake valve cams or the pair of exhaust valve cams with being interposed between these cams, and more specifically the bearing portion is located in the outboard region of a cylinder and at a position corresponding to the center of said cylinder.
However, in case that a variable valve timing (VVT) control and/or variable valve lift (VVL) control device for varying the valve timing and/or valve-lift amount of the intake and/or exhaust valves in response to driving conditions is applied to improve fuel consumption and output power, a plurality of cams each having a different cam profile in valve-opening timing or valve-lift amount, for example, are provided for each valve, and this results in the increased number of cams for each cylinder. For example, in the above-exemplified engine, the bearing portion may be hardly to be arranged at the position corresponding to the center of the cylinder, and thereby will be arranged between adjacent cylinders. In this case, if the number of cams for each valve is not more than two, the bearing portion is not required to locate excessively far from the position corresponding to the center of the cylinder. However, if the number of cams for each valve is increased, for example, up to 3 or more, the bearing portion is required to locate far from the position corresponding to the center of the cylinder and consequently locates at approximately middle position between the cylinder and another cylinder adjacent to the cylinder.
Unfortunately, in the middle portion between adjacent cylinders, a cylinder head bolt for securing the cylinder head to a cylinder block is necessarily located to evenly receive the stress due to the combustion pressure in the cylinder, which leads to the interference between the cylinder head bolt and the bearing portion. For measures to this problem, the cylinder head may be fastened to a cylinder block by using in common a bolt for uniting the cam cap with the vertical wall portion. However, this undesirably results in a lengthened cylinder head bolt and excessively enlarged bearing portion.
On the other hand, separately mounting the vertical wall portion or tappet guide to the cylinder head leads to the increased number of parts, a complexified cylinder head structure, and a lowered flexibility of cylinder head layout. This causes problems, such as the significantly increased volume and height of the cylinder head. Further, in the engine having the variable valve control device, the cylinder head is required to firmly support associated components including an oil pressure control valve for supplying an operating oil to a movable portion of the device.
A technique for reducing the number of parts of the cylinder head is, for example, disclosed in Japanese Patent Laid-Open Publication No. Hei 7-103068 wherein a cam cap for supporting the upper portion of a camshaft reliably secures a plug tube for an ignition plug to a cylinder head by pressing the plug tube in its axial direction with constraining the plug tube in its radial direction. Japanese Patent Laid-Open Publication No. Hei 5-86813 also discloses a related technique wherein an ignition-plughole is comprised of a lower ignition-plug hole formed in a cam carrier for supporting the lower portion of a camshaft and an upper ignition-plug hole formed in a cam cap for supporting the upper portion of the camshaft. However, these techniques cannot solve the above problems all at once.
It is known that a carrier member integrally including a vertical wall portion defining a bearing portion for a camshaft and a tappet guide for containing a tappet is formed separately to a cylinder head. For example, Japanese Patent Laid-Open Publication No. Hei 6-146822 discloses a related technique wherein a cam carrier integrally including at least a camshaft journal and a lifter guide portion is formed separately to a cylinder head, and the cam carrier is integrally fastened to a cylinder head body. Japanese Patent Laid-Open Publication No. Hei 8-74540 also discloses a related technique wherein a cam carrier having a plurality of cam bearing portions integrally connected with each other by guide bosses formed with lifter guide holes is prepared as respective intake and exhaust cam carriers to be mounted separately to a cylinder head.
Further, Japanese Patent No. 259735 discloses a related technique wherein a camshaft bearing pedestal doubling as a support member of a tappet is connected to a cylinder head. Japanese Patent Laid-Open Publication No. Hei 4-91351 also discloses a related technique wherein a carrier supporting a camshaft and formed with a tappet-carrying device is mounted on a cylinder head. Furthermore, Japanese Patent Laid-Open Publication No. Hei 11-148426 discloses a cylinder block on which an oil pressure control valve of a variable valve-timing (VVT) control device.
All of these techniques disclosed in the above publications are intended to assure the supporting rigidity of the camshaft and tappet. In case of housing the aforementioned variable valve control device in the tappet, it is required to comprehensively consider the oil distribution for overall valve system including the lubrication of the tappet itself and the camshaft in addition to the above object. However, any construction for achieving these needs is not discussed in the above publications.
For example, in the construction disclosed in Japanese Patent Laid-Open Publication No. Hei 6-146822, the surrounding sidewall of the lift guide portion extends obliquely upward to form a receiving region for receiving a lifter lubricating-oil. However, since the cam carrier disposed on the exhaust side employs a so-called inter-port bearing, or a camshaft journal is arranged between two adjacent lifter guide portions, it is difficult to arrange a plurality of cams for one valve. Thus, this construction is not inherently suitable for engines equipped with the aforementioned variable valve control device. Further, in case of applying the aforementioned variable valve control device, this publication discloses or suggests neither method for supplying operating oil to the device nor its presupposed element, such as an arrangement of lubrication oil channels of the camshaft.
Japanese Patent Laid-Open Publication No. Hei 8-74540 discloses a variable valve timing control device, a valve intermitting (valve stop) device, and an oil supply passage for the valve intermitting device provided in the can carrier and located in parallel with the camshaft. However, this publication does not discuss any lubrication oil channel for the camshaft, the tappet, and other fundamental components. Japanese Patent No. 259735, Japanese Patent Laid-Open Publication No. Hei 4-91351, and Japanese Patent Laid-Open Publication No. Hei 11-148426 do not describe any construction for lubricating the tappet.
In view of the aforementioned problems, it is an object of the present invention to provide an improved cylinder head capable of avoiding the interference between a cylinder head bolt and a camshaft bearing portion and achieving the reduced number of parts, an enhanced flexibility of layout, and an improved supporting rigidity.
It is another object of the present invention to provide an improved cylinder head structure including a tappet which houses a variable valve control device, capable of assuring a sufficient supporting rigidity of the tappet, camshaft, or the like, and comprehensively satisfying the oil distribution for an overall valve system including the operating oil supply to the variable valve control device, or the lubrication oil supply to the tappet or camshaft.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided a cylinder head structure for an engine including a tappet which houses a variable valve control device for varying at least one of valve-lift amount and valve-opening timing. The cylinder head structure comprises a carrier member integrally formed with a vertical wall portion located between adjacent cylinder bores and having a bearing portion for supporting a camshaft and a tappet-carrying portion for containing the tappet for intake port or exhaust port. The carrier member is formed separately to a cylinder head. The cylinder head structure further comprises an oil supply passage for the variable valve control device, provided in the carrier member at the position closer to the central region of the carrier member than the position of the tappet-carrying portion. The oil supply passage extends along the direction in which the tappet-carrying portion is arranged in the carrier member. The cylinder head structure further comprises an oil-receiving portion for receiving a tappet-lubricating oil, provided in the periphery of the tappet-carrying portion. The oil-receiving portion couples the tappet-carrying portion with the vertical wall portion, and the marginal region of the oil-receiving portion is directed upward.
According to the first aspect of the present invention, the cylinder head structure includes the carrier member integrally formed with the vertical wall portion located between adjacent cylinder bores to support the camshaft and a tappet-carrying portion for containing the tappet for each intake or exhaust port, wherein the carrier member is formed separately to a cylinder head. Thus, the vertical wall portion defining a bearing portion and the tappet-carrying portion for guiding the tappet may be mounted to the cylinder head at once only by mounting the carrier member to the cylinder head. This allows the cylinder head structure to have the reduced number of parts, a simplified structure, and an enhanced layout performance. As a result, an enhanced assembling operation performance and a sufficiently downsized cylinder head structure may be achieved.
In this carrier member, since the vertical wall portion and tappet-carrying portion each having a different configuration are connected with each other, the carrier member may have a higher rigidity or stiffness by a complementary relationship therebetween. This may improve the supporting rigidity of the camshaft, tappet, oil-pressure control valve of the variable valve control device or the like.
Further, since the carrier member is formed separately to the cylinder head, the bearing portion defined by the vertical wall portion may avoid interfering with the cylinder head bolt and thereby the flexibility of the arrangement of the bearing portion is not restricted by the presence of the cylinder head bolt. Thus, the bearing portion may, for example, be arranged overlappedly above the head bolt without any trouble.
In addition to the above structure, the oil supply passage for the variable valve control device extends along the direction in which the tappet-carrying portion is arranged. Thus, sufficient operating oil may be supplied to the device, while the rigidity or stiffness of the carrier member may further be enhanced.
Further, since the oil-receiving portion for receiving the tappet-lubricating oil is provided around the tappet-carrying portion, the tappet may be adequately lubricated by the oil collected in the oil-receiving portion (external lubrication system). In addition, any dedicated oil supply passage is unnecessary to be formed in the carrier member so that the carrier member may avoid to be complexified in structure and may be readily manufactured.
Furthermore, since this cylinder head structure is applied with a so-called inter-bore bearing; specifically the vertical wall portion for supporting the camshaft is arranged between the adjacent bores, the overall valve system may be compactly arranged. As described above, according to the first aspect of the present invention, an improved carrier member having compact size and reliable rigidity and a sufficient oil distribution to the variable valve control device and tappet may be satisfied all at once.
In one specific embodiment, the oil supply passage for the variable valve control device may include a branched passage extending in the lateral direction of the carrier member, wherein the branched passage is configured to provide fluid communication with the tappet-carrying portion so as to supply oil to the variable valve control device.
According the above structure, the operating oil may be supplied to the variable valve control device through the oil supply passage for the variable valve control device. For example, when one branched passage has fluid communication with one tappet-carrying portion, said one tappet-carrying portion may be supplied with oil through said one branched passage. This allows the variable valve control device to be individually operated. Otherwise, when one branched passage has fluid communication simultaneously with a plurality of tappet-carrying portions, said one branched passage may introduce oil to the plurality of tappet-carrying portions so as to simultaneously operate a plurality of variable valve control devices.
In another specific embodiment of the present invention, the camshaft may further be provided with an inner oil channel extending in the longitudinal direction of the camshaft and an branched oil channel branched from the inner oil channel at the portion where the camshaft is supported by the bearing portion, so as to be opened at the peripheral surface of the camshaft. Further, the bearing portion is provided with an inner groove opposed to the opening. Furthermore, a camshaft-lubricating oil channel is provided in the bearing portion supporting the edge of the camshaft. The camshaft-lubricating oil channel is configured to provide fluid communication with the inner groove.
According the above structure, a sufficient lubrication to the camshaft may be achieved by providing the particular oil channels and inner groove in the conventional camshaft and bearing portion. In addition, any dedicated member is not additionally required so that the carrier member may avoid to be complexified in structure and may be readily manufactured.
According to a second aspect of the present invention, there is provided a cylinder head structure for a DOHC engine including a tappet which houses a variable valve control device for varying at least one of valve-lift amount and valve-opening timing. The cylinder head structure comprises a carrier member integrally formed with a vertical wall portion located between adjacent cylinder bores to support a camshaft and a tappet-carrying portion for containing the tappet for each intake or exhaust port located between the vertical wall portions adjacent to each other. The carrier member is formed separately to a cylinder head. The cylinder head structure further comprises a cam cap for supporting the camshaft in cooperation with the vertical wall portion. The cam cap is coupled with the vertical wall portion. The cylinder head structure further comprises an oilreceiving portion for receiving a tappet-lubricating oil, provided around the tappet-carrying portion of the carrier member. The oil-receiving portion couples the tappet-carrying portion with the vertical wall portion, and the marginal region of the oil-receiving portion is directed upward.
According to the second aspect of the present invention, the same effects as those of the first aspect of the present invention may be yielded in the DOHC engine. In particular, applying the inter-bore bearing allows cams provided in the camshaft to be arranged to the intake and/or exhaust port or the tappet-carrying portion with high flexibility, and thereby the variable valve control device may be freely mounted to the cylinder head structure even if the variable valve control device includes a plurality of cams for each valve.
In addition, the oil-receiving portion for receiving the tappet-lubricating oil is surrounded by the marginal region directed upward and the vertical wall portion which is increased in height by connecting the cam cap thereto, and the corresponding bearing portion is used as a oil separator. Thus, the oil collected in the oil-receiving portion may avoid to be excessively reduced and thereby sufficient lubrication of the tappet may be reliably maintained even by the external lubrication system.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description.